1. Field of the Invention
The present invention relates to a monitor that can detect trace molecules from a sample. By way of example, the monitor may be a mass spectrometer.
2. Background Information
Mass spectrometers are typically used to detect one or more trace molecules from a sample. For example, a mass spectrometer can be used to detect the existence of toxic or otherwise dangerous compounds in a room. Mass spectrometers are also used to analyze drug compounds in solvents. Mass spectrometers typically ionize trace molecules from a gas sample and then deflect the ionized molecules into a detector. The detector may detect the mass of the ionized molecule by measuring the time required for the molecule to travel across a chamber or by other means. The identity of the molecule can then be determined from the mass.
U.S. Pat. No. 5,808,299 issued to Syage discloses a mass spectrometer that contains a photoionizer. The photoionizer includes a light source that can emit a light beam into a gas sample. The light beam has an energy that will ionize constituent molecules without creating an undesirable amount of fragmentation. The molecules are ionized at low pressures. Low pressure ionization is not as effective in detecting small concentrations of molecules.
U.S. Pat. No. 4,849,628 issued to McLuckey et al. (xe2x80x9cMcLuckeyxe2x80x9d) discloses a mass detection system that can detect relatively low concentrations of a trace molecule. McLuckey utilizes a glow discharge ionizer that ionizes an xe2x80x9catmosphericxe2x80x9d sample. Providing an air sample at atmospheric pressures increases the density of the sample and the number of ionized molecules. Increasing the number of ions improves the sensitivity of the detector. Although McLuckey uses the term atmospheric, ionization actually occurs in an ionization chamber having a pressure between 0.1 to 1.0 torr.
It is generally desirable to provide a mass spectrometer that can detect a number of different compounds; provides a strong molecular ion signal with minimal fragmentation; is not susceptible to interference and gives a linear response with concentration.
It would be desirable to provide a photoionizer that can handle large quantities of sample in order to use with various liquid flow sources such as liquid chromatography and separation columns. It would also be desirable to provide a photoionizer that ionizes analyte in liquid samples by a means other than thermal vaporization.
One embodiment of the present invention is a monitor that can detect a trace molecule in a sample provided by an inlet at approximately one atmosphere. The trace molecule can be ionized by a photoionizer coupled to the inlet. The trace molecule can be detected by a detector.